(1) Field of the Invention
The present invention relates to a novel collagen powder, a leather-like surface layer-forming agent comprising this powder, and a leather-like molded article.
(2) Description of the Related Art
In the fields of sheets such as vinyl chloride sheets and artificial leathers, nonwoven fabrics, furniture and household electric appliances, recent trends toward a higher quality have brought about a demand for sheet surfaces having the appearance, feel, and functions resembling those of natural leather. To meet this requirement, a process has been proposed in which a collagen powder such as a leather fiber powder or a leather powder formed by pulverizing leather scraps is used together with a synthetic polymeric resin such as a polyurethane resin, a polyester resin, a polyacrylic resin, a polyvinyl chloride resin or a polyolefin, or a synthetic rubber such as an SB rubber, to form a covering layer on the surface of an automobile interior trim, a construction interior material, furniture or a precision machine, or to form a molded article such as a steering wheel cover of an automobile, whereby performances resembling those of natural leather are imparted thereto.
Various proposals have been made for the above-mentioned collagen powder, such as the leather fiber powder or leather powder disclosed, for example, in Japanese Unexamined Patent Publication No. 49-7405, Japanese Unexamined Patent Publication No. 63-218286, and Japanese Unexamined Patent Publication No. 63-236636. In the collagen powder disclosed in Japanese Unexamined Patent Publication No. 49-7405, since the size of the collagen fiber is large, i.e., 80 mesh (180 .mu.m), where the collagen powder is used together with a thermoplastic resin powder for preparing a sheet-like artificial leather, complicated steps are necessary for obtaining a leather-like covering layer. In Japanese Unexamined patent Publication No. 63-218286, as in the above-mentioned patent publication, the leather powder is particulate and the maximum particle size is 150 mesh (100 .mu.m), and therefore, a dry, smooth feeling cannot be obtained, and the moisture-absorbing or moisture-releasing property thereof is poor. Also, since the collagen powder disclosed in Japanese Unexamined Patent Publication No. 63-236636 is a leather powder obtained merely by pulverizing leather scraps, the tanning treatment is conducted on the leather powder in the state of a hide, and thus the leather fiber is not uniformly tanned. Accordingly, the water absorption of the powder is lower than 120% by weight and the apparent bulk density (JIS K-6721) is larger than 0.30 g/cc, and accordingly, the powder is defective in that the moisture-absorbing and moisture-releasing properties are poor. Moreover, since the oil absorption (JIS K-5101) is low, the collagen powder is sedimented in a resin or a resin solution because of the difference between the true density of the collagen powder and the density of the resin solution, and the powder is caked and cannot be re-dispersed. Namely, the collagen powder has a poor dispersion stability. Therefore, the collagen powder is unsatisfactory for practical use.
No standardized method for measuring the water absorption of a powder has been set as yet, and accordingly, the following method is adopted in the present invention. Namely, 1.0 g (Wa) of a powder sample is immersed in water for more than 1 hour, to absorb the water in the sample, and the sample is then thoroughly drained and is placed in the form of a circle having a diameter of 4 cm, on a filter paper (Filter Paper No. 5C supplied by Toyo Roshi; diameter 9 cm). Several filter papers are laminated above and below the sample, a weight of 20 kg is placed on the assembly, and a dehydration under compression is carried out for 3 minutes to remove excess water adhering thereto. The weight (Wb) of the sample is then measured, and the water absorption is calculated according to the following formula: ##EQU1##